Method of operating a hydraulic device



Feb. 24, 1970 Filed July 14, 1967 R. B. M EUEN METHOD OF OPERATING A HYDRAULIC DEVICE 2 Sheets-Sheet l all INVENTOR. F0559? 5 M: EUEA/ Feb. 24, 1970 Filed July 14, 1967 R. B. M EUEN METHOD OF'OPERAT ING A HYDRAULIC DEVICE 2 Sheets-Sheet z INVENTOR. 19055 87 5. M: EOE/v United States Patent 3,496,837 METHOD OF OPERATING A HYDRAULIC DEVICE Robert B. McEuen, La Habra, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California Filed July 14, 1967, Ser. No. 653,360 Int. Cl. FlSb 13/02; F17d 1/16, 1/18 U.S. Cl. 91-471 8 Claims ABSTRACT OF THE DISCLOSURE Method of operating a hydraulic device, e.g., a vibrator, that employs electrical energy for production or modulation of hydraulic power, comprising controlling or adjusting the production or modulation by means of an electric signal generated by shear of the hydraulic fluid employed in the device.

This invention relates to hydraulic devices employing electric fields for control of hydraulic power and methods of operating such devices. More particularly, the invention relates to methods for controlling or adjusting electric field-modulation of the hydraulic power of such a device. The invention is particularly applicable to hyrdaulic devices employing electroviscous fluids, i.e., fluids whose viscosity increases rapidly but reversibly on application of an electric field.

The term hydraulic device as employed in the specification and claims is intended to include any device in: which a liquid or fluid is used to generate or transfer energy in a system. Examples of such devices are vibrators, clutches, brakes, chucks, pumps, valves, fluid logic devices, etc.

Vibrators employing electroviscous fluids are described in the September 1966 issue of Hydraulics and Pneurn'atics (vol. 19, No. 9, pages 139-143). These devices utilize valves consisting of narrow passageways through which an electroviscous fluid flows. When an electric field is applied across the fluid moving through the valves the field produces variations of fluid viscosity within the valve passageways, thus producing variations in pressure drop across the valves. This pressure drop is utilized to apply a force to a driving member such as a piston. By applying input voltage Waveforms corresponding to the desired piston motion, the devices can be made to act as a fast-response hydraulic actuator. Such devices are of increasing importance to the aerospace industry in missile and space vehicle development programs.

For most purposes it is desirable that the acceleration of the piston, or other driving member, be proportional to the input voltage and that the waveshape of the acceleration reproduce that of the input signal, with low distortion. These objectives are conventionally achieved by means of acceleration feedback. As described in Air Force Systems Command Technical Documentary Report No. ASD-TDR-62-536, August 1962, one possible source of feedback is an alternating voltage generated by an accelerometer attached to the piston. This voltage is amplified and compared with the input signal voltage. The error voltage is then amplified and fed to the valves in such a way as to reduce the distortion, i.e., to reduce the deviation of output acceleration and waveshape from that of the input signal. This procedure, however, has the disadvantage of requiring an additional, separate device, the accelerometer, which must be attached to the output piston and provision made for the necessary leads from accelerometer so as not to interfere with the movement of the piston.

It has now been found that a much simpler and more economical source of feedback is obtained by utilizing the electrical signal developed by shear of the electroviscous fluid resulting from variation in flow rate of the fluid in the hydraulic device. This variation in flow rate results from the change in viscosity of the electroviscous fluid in the valves in response to the input signal across the valves and is functionally related to the input signal. The feedback signal is generated by change in the electrical properties of the fluid and is functionally related to the shear rate of the electroviscous fluid, which in turn is determined by the change in displacement of the driving member. The entire system thus comprises a closed loop in which the electroviscous fluid responds to the change in voltage of the input signal, thereby modulating the hydraulic power supplied by a hydraulic pump, and also generates the feedback voltage for reduction of distortion in the response to the input voltage. This system will be described in more detail with reference to FIGURE 1.,

The invention can be best understood by reference tothe drawings of which;

FIGURE 1 is a schematic illustration of a hydraulic transducer, fluid pump and shear responsive probe.

FIGURE 2 is a cross sectional illustration of a signal generating shear responsive probe.

FIGURE 3 is an electronic circuit suitable for controlling the several elements of the hydraulic transducer.

FIGURES 4-7 are graphic illustrations of the voltage response at several points in the control circuit of FIG- URE 3.

FIGURE 1 shows a device of the type disclosed in the prior art modified according to applicants invention. The device comprises (1) the vibrator assembly, (2) the associated hydraulic lines including a suitable hydraulic pump and (3) mechanical and electrical elements for detecting theelectric signal generated by shear of the hydraulic fluid in accordance with 'applicants invention. The vibrator assembly is indicated generally by reference 1 and consists of cylinder 2, output shaft 3 and valves (not shown in drawing) located within cylinder 2.

Electroviscous fluid from constant-flow pump 4 flows through hydraulic line 5 and enters the center of cylinder 2 at port 6, divides and, when no voltage is applied, flows in equal amounts through the valves to exhaust ports 7 and 8 at the ends of the cylinder. The fluid is then recirculated to the pump via hydraulic lines 9 and 10.

Control voltages (input signal), which are applied to the valves may take a variety of forms but are generally sine waves or square waves combined with a D-C bias.

According to the present invention the prior art device of FIGURE 1 is modified by insertion of a probe, e.g., reference 11, in one of the hydraulic lines. For purposes of illustration'the probe is shown in line 10, but it may be located at any point in the hydraulicoutput lines since the flow-rate of the hydraulic fluid at -any point is proportional to the output (velocity wave form of the output shaft) of the device. Details of one example of probe 11 that may be used in the invention are shown in crosssection in FIGURE 2. The probe consists of inner and outer concentric cylindrical electrodes, 12 and 13, fabricated of a conducting material such as steel. Other materials that may be used are copper, platinum, etc. Inner electrode 12 is mounted concentrically with respect to electrode 13 by means of spacers 14 and 15 which are fabricated of any suitable insulating material such as Scotch Cast or Teflon and are in the form of spokes to allow unimpeded flow of fluid in passageway 16 defined by the electrodes. Spacers 14 and 15 also serve to insulate electrode 13 from cyclindrical connecting sections 17 and 18, which are provided with threaded ends for attachment in hydraulic line 10. Electrical leads 19 and 20 are attached to electrodes 12 and 13, respectively, lead 19 passing through a hole in electrode 13 and electrically insulated therefrom by means of insulating material 21. The optimum area-to-gap ratio for the probe is highly variable. One configuration similar to that shown in FIG- URE 2 had a ratio of 250 inches. This ratio will of necessity vary with resistivity of the hydraulic fluid. A useful range of ratios would be from about 100 to 10,000 inches.

As the electroviscous fluid passes through probe 11 it is sheared at a rate proportional to its flow rate, which is in turn functionally related to the velocity of the output shaft. This variation in shear rate results in a change in the fluids electrical admittance between electrodes 12 and 13 and this change in admittance is subsequently utilized for developing feedback signal for reduction of distortion in response to the input voltage.

The specific design features of the probe may vary widely and numerous embodiments, other than the one specifically described above, will be apparent to one of ordinary skill in the art. For example, cylindrical sections 13, 17 and 18 may be a single unit, constructed of a conducting material, and fitted to hydraulic lines constructed of a non-conducting material. Shape and dimensions of both the inner and outer electrodes may vary widely for optimum results depending on a variety of factors such as type of fluid, rate of fluid flow, pressure of fluid, etc. Furthermore, the use of inner and outer, concentric electrodes is not essential, the only requirement being the provision of two electrically insulated electrodes between which the electroviscous fluid may flow. Other possible electrode arrangements employ nested cylinders or a configuration in which the outside cylinder is at ground potential and in which elements 14 and 15 merely insulate cylinder 12.

Circuits suitable for producing a feedback signal and comparing it with the input voltage to the hydraulic device do not constitute a part of the present invention and may be readily designed by one of ordinary skill in the art. An example of such a circuit is shown in FIGURE 3. The circuit shown in this figure also includes provision for detection of a D-C signal for control of operating temperature of the device, as more fully described below.

In FIGURE 3, leads 19 and 20 (ground), connect to a circuit comprising DC. power supply or battery 22, capacitors 23 (-0.002 ,ufd.) and 24 (100 nfd.), resistors 25 (8K), 26 (M), 27, 28 and 29, variable resistors 30 (5M) and 31 (1009), transformer 3 having primary winding 33 and secondary winding 34, rectifiers 35 and 36, and triode vacuum tubes 37 and 38. Exact values of resistors 27, 28 and 29 will vary according to the characteristics of vacuum tubes 37 and 38 and may be readily determined by one of ordinary skill in the art. Simultaneously, a portion, V,, of the input voltage to the hydraulic device is fed via transformer 39 and rectifiers 40 and 41 to the grids and cathodes of tubes 37 and 38. By means of these circuits a voltage, V,, proportional to the error in the fluids acceleration (as compared to the input voltage) is produced between points 42 and 43 of the circuit. This error voltage is then utilized in conventional circuits, with amplification if necessary, to change the gain of the power amplifier (not shown in drawings) by means of which a suitably modulated input signal is fed to the hydraulic device. In this way the acceleration error may be reduced to substantially zero.

The voltage appearing across points 44 and 45 is proportional to the admittance, Y, of the gap through which across points 44 and 45 above the static value indicate increases in the average velocity of the fluid in the gap.

Reduction of the fluids acceleration error to zero is accomplished by comparison of the full-wave rectified derivative of the voltage across points 44 and 45 with the full-wave rectified version of the input voltage to the device. The derivative of the voltage across points 44 and 45 appears across resistor 31 when 1/ jaw is much greater than the value of resistor 31, where w=21r (frequency), j= I and c is the value of capacitor 23. FIGURE 4 shows the wave form of the voltage across points 44 and 45 for simple harmonic fluid flow and FIGURE 5 shows the derivative of this voltage (V which appears across resistor 31.

The voltage appearing at the secondary of transformer 32 has the same form as that across resistor 31. This voltage undergoes full wave rectification and amplification between the secondary and point 42. This results in a waveform at point 42 as shown in FIGURE 6.

If the acceleration of the fluid corresponds to the input voltage, the voltage at point 42 will be identical to the voltage at point 43, which is a full wave rectified version of the input voltage. For this condition the error voltage V,,, i.e., the voltage across points 42 and 43, will be zero. In practice resistor 31 is adjusted to make V,, as small as possible. Via feedback, V is used to change the gain of the power amplifier and reduce the fluids acceleration error to zero.

As stated above, one advantage of applicants invention is that it enables simultaneous control of temperature of operation of the device and of output acceleration distortion. Temperature control is possible since direct current through the probe is a function of temperature while, as described above, alternating current through the probe represents change in the absolute value of the fluids velocity. Temperature control is achieved by means of output V (FIGURE 3) across resistor 30, this voltage being proportional to the temperature of the fluid. As the hydraulic device does work the temperature of the electroviscous fluid slowly increases and the fiuids admittance per unit volume increases with the increase in temperature. Thus, the voltage appearing across points 44 and 45 will increase and appear as shown in FIGURE 7a. The rapidly varying component of this voltage is removed by the low pass filter consisting of resistors 25, 26 and 30 and capacitor 24. The remaining D-C voltage, V shown in FIGURE 7b, is essentially a monotonic function of temperature and can be used to control cooling equipment (not shown in drawings) and maintain the device at constant temperature. Suitable cooling devices will be obvious to one skilled in the art and do not constitute part of the present invention. They may be similar to those used with thermocouples or the voltage V can be power amplified and applied directly to a thermoelectric cooling device.

Electroviscous fluids and their properties are disclosed in U.S. Patents 3,047,507, 3,250,726, 3,279,496 and 3,309,915. They consist of a suspension of particulate nonconducting particles in an oleaginous vehicle and may contain various other materials such as surface active agents, organic acids and amines for achieving optimum reaction of the fluid to the applied electric field. It has been found that fluids in which the particulate material is high-silanol silica, of the type described in,

High-silanol silica 52.00 vis neutral oil 33.60 Glycerol monooleate 12.40

Although the invention finds particular utility in a vibrator of the type described above, employing an Acetic acid electroviscous fluid, it is applicable to any device in which hydraulic power is produced or modulated by means of electric power and in which the hydraulic fluid is shear-responsive, i.e., it exhibits changes in electrical properties when subjected to shear. These electrical properties may include, e.g., conductivity or production of an induced potential. Examples of such devices are, as stated above, clutches, brakes, valves, chucks, pumps, fluid logic devices, etc. Examples of suitable shearresponsive hydraulic fluids, other than the electroviscous fluids described above, are fluids made from vanadium pentoxide. An example of such a fluid has the followin composition: 7

Weight percent Vanadium pentoxide 57.2.0 #2 white oil 42.74 Glycerol monooleate .06

I claim:

1. A method of operating a hydraulic device using electrical energy for modulation of hydraulic power comprising controlling or adjusting said modulation by means of an electric signal generated by shear of the hydraulic fluid in said device.

2. The method of claim 1 additionally including controlling the temperature of the device by cooling means controlled or adjusted by variation of a direct current component of the current through the hydraulic fluid.

3. The method of claim 1 in which the hydraulic fluid is an electroviscous fluid.

4. The method of claim 2 in which the hydraulic fluid is an electroviscous fluid.

5. The method of claim 1 in which the modulation of the hydraulic power in the device is obtained by means of application of an electric field to a hydraulic fluid consisting essentially of an electroviscous fluid.

6. The method of claim 2 in which the modulation of the hydraulic power in the device is obtained by applica" tion of an electric field to a hydraulic fluid consisting essentially of an electroviscous fluid.

7. The method of claim 5 in which the electroviscous fluid comprises a suspension of high-silanol silica in a mineral oil.

8. The method of claim 6 in which the electroviscous fluid comprises a suspension of high-silanol silica in a mineral oil.

References Cited UNITED STATES PATENTS 2,417,850 3/1947 Winslow 317-14.4 2,661,596 12/1953 Winslow 52 3,250,726 5/1966 Martinek et al. 252317 3,279,496 10/ 1966 Klass et al. 137487.5 3,302,532 2/1967 Graham l37-13 X 3,327,223 6/1967 Halista l37-81.5 X

OTHER REFERENCES Hydraulics and Pneumatics, September 1966, vol. 19, No. 9, pp. 139-143.

CARROLL B. DOR'lT Y, JR., Primary Examiner US. Cl. X.R. 

